Events event tree analysis

Layer of protection analysis (LOPA) is a simplified form of event tree analysis. Instead of analyzing all accident scenarios, LOPA selects a few specific scenarios as representative, or boundary, cases. LOPA uses order-of-magnitLide estimates, rather than specific data, for the frequency of initiating events and for the probability the various layers of protection will fail on demand. In many cases, the simplified results of a LOPA provide sufficient input for deciding whether additional protection is necessary to reduce the likelihood of a given accident type. LOPAs typically require only a small fraction of the effort required for detailed event tree or fault tree analysis. 

A simplified form of event tree analysis using selected accident scenarios and order-of-magnitude estimates to determine whether additional protection is needed... 

Recognized systematic approaches include hazard operability study (HAZOP) event tree analysis fault tree analysis. 

Chapter 12 discusses the distribution software BETA for preparing event tree analysis from a work processor table. BETA allows the use of binary conditionals so the nodal probabilities in a vertical line are not necessarily equal but depend on preceding events. 

Step I - Select the combinations of systems that enter the analysis. (This is equivalent to finding accident sequences in event tree analysis.)... 

RISKMAN is an integrated Microsoft Windows , personal computer software system for [H. i forming quantitative risk analysis. Used for PSAs for aerospace, nuclear power, and chemical [iroccsses, it has five main modules Data Analysis, Systems Analysis, External Events Analysis, Event Tree Analysis, and Important Sequences. There are also modules for software system maintenance, backup, restoration, software updates, printer font, and page control. PEG has also integrated the fault tree programs CAFTA, SETS, NRCCUT, and IRRAS into RISKMAN. 

Wyss, G. D. et al., 1990, Accident Progression Event Tree Analysis for Postulated Severe Accidents at N-Reactor, SNL, SAND89-2100. 

Event Tree Analysis (ETA) A method for illustrating the intermediate and final outcomes that may arise after the occurrence of a selected initial event. 

Perform an event tree analysis to find tire path(s) an accident may follow... 

Perhaps the key to detcrnuiiiiig die consequences of an accident is die study of accident mininiization/prcvendon. This topic receives extensive treatment in Section 17.2. The estimation (not calculadon) of consequences is treated in Section 17.3, which is followed by evacuation procedures (Section 17.4). The next section e.xaniiiies failure modes, effects and critical analysis (FMECA). The cluipter concludes with vulnerability analysis (Section 17.6) and event tree analysis (Section 17.7). 

Figures 17.7.1 and 17.7.2 present a sample event tree analysis and an example of an event tree for a dmiii rupture.

Describe staffing requirements for an event tree analysis. 

A single analyst can perform an event tree analysis, but nonnally a team of 2 to 4 people is preferred. The team approach promotes "brainstonning" tliat results in a well defined event tree structure. The team should include at least one member witli knowledge of event tree analysis, witli tlie remaining members having e.xperience in tlie operations of tlie systems and knowledge of the chemical processes that are to be of interest in tlie analysis. 

Event tree analysis is a teclmique for evaluating potential accident outcomes resulting from a specific initiating event. Tlie results of the event tree analysis are clironological sets of failures or errors that may define an accident. 

In a more quantitative sense, cause-consequence analysis may be viewed as a blend of fault tree end event tree analysis (discussed in tlie two preceding cliapters) for evaluating potential accidents. A major strengtli of cause-consequence analysis is its use as a communication tool. For example, a cause-consequence diagram displays the interrelationships between tlie accident outcomes (consequences) and Uieir basic causes. The method can be used to quantify the expected frequency of occurrence of the consequences if the appropriate chita are available. 

In Section 21.4 tlie effects of the release of toxic vapors were considered in connection witli an accident sequence initiated by the failure of a plant programmable automatic controller. In tliis study, event tree analysis and fault tree analysis led to identification of tlie glycol cooling system circulation pumps as components meriting high priority for inspection. 

Event tree analysis adapted to accidental hydrogen releases. (From Rigas, F. and Sklavounos, S., lnt. ]. Hydrogen Energ., 30,1501,2005. With permission from International Association of Hydrogen Energy.)... 

Event Tree Analysis (ETA) is suggested by the DOE-STD-1027-92, but not included in the PSM Rule. However, the PSM Rule does allow the use of "an appropriate equivalent methodology." Hence, if ETA is to be used as the PrHA, the PrHA report must justify that the ETA method is appropriate and equivalent to the methods listed in the rule. 

The typical steps in an event tree analysis are3... 

This event tree analysis shows that a dangerous runaway reaction will occur on average 0.025 time per year, or once every 40 years. This is considered too high for this installation. A possible solution is the inclusion of a high-temperature reactor shutdown system. This control... 

Event tree (analysis) a graphical logic diagram which identifies and sometimes quantifies the frequencies of possible outcomes following an initiating event. 

Layer-of-protection analysis (LOPA) A method, based on event tree analysis, of evaluating the effectiveness of independent protection layers in reducing the likelihood or severity of an undesired event. 

The starting point in event tree analysis is the initiating event. The quantitative evaluation of the event tree requires condition probabilities. These may be based on reliability data, historical records, experience, or from fault trees. 

Additional models and software are identified in A Guide to Quantitative Risk Assessment for Offshore Installations (Spouge, 1999) which address offshore risk analysis, explosion modeling, evacuation and rescue analysis, reliability analysis, accident databases, event tree analysis, and safety management. 

Other examples of inductive tools that have limited application in incident investigation include failure mode and effects analysis (FMEA), hazard and operability study (HAZOP), and event tree analysis (ETA). These are detailed in the CCPS book, Guidelines for Hazard Evaluation Procedures... 

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